The beginning of the 21st century viewed a significant development of user wireless terminals for both fixed and mobile environments. For example, the modern PCs (personal computers) and notebooks (laptops) are enabled with wireless connections to allow for some mobility and reduce the wiring between the components of the PC. Home LAN convergence rapidly integrated home routers, wireless access points and DSL modems to connect home computers to a subscribed Internet service. In response to the growing demand for broadband connection to user premises, a worldwide trend became apparent, namely a move from analog to digital TV Digital (DTV). DTV has several advantages over analog TV. Thus, DTV is more flexible and efficient than analog television; it enables special services such as multiplexing (more than one program on the same channel), electronic program guides and additional languages, spoken or subtitled. Another significant advantage of the DTV is that the digital channels take up less bandwidth and provide a better performance. This means that digital broadcasters can provide high definition (HDTV) services, with higher-quality images and sound. The sale of non-television services may also provide an additional revenue source.
In the US, the FCC mandated transition to digital TV (DTV). Conversion to DTV results in important bandwidth becoming free in the VHF (very high frequency) and/or the lower part of the UHF (ultra high frequency) spectrum, used currently by TV broadcasters. As each TV station operating in a certain geographic region/area (TV market) uses only a limited number of channels from the TV band, some digital channels remain unused by broadcasters in the respective area: this locally available spectrum is called “white space”.
For example, in the United States there are roughly 210 TV broadcast markets and 1700 TV broadcasting stations. Currently, each TV station is assigned around eight radio frequency (RF) channels for NTSC broadcast, each channel occupying 6 MHz in the VHF/UHF spectrum. The Federal Communications Commission (FCC) has mandated that all full-power television broadcasts will use the Advanced Television Systems Committee (ATSC) standards for digital TV by no later than Feb. 17, 2009. These developments open the way to providing a variety of new, dedicated services to individual/family subscribers. The FCC intends to allocate channels 2 through 51 to digital TV; channels 52 through 69 that occupy the lower half of the 700 MHz band have already been reallocated through auction to various advanced commercial wireless services for consumers. When transition DTV ends in early 2009, every one of the 210 TV markets in the US will have 15 to 40 unassigned (vacant) channels reserved for broadcasting, but not in use. Vacant TV channels are perfectly suited for other unlicensed wireless Internet services. Access to vacant TV channels facilitates a market for low-cost, high-capacity, mobile wireless broadband networks, including the emerging in-building networks. Using this white space, the wireless broadband industry could deliver Internet access to every household for as little as $10 a month by some estimates.
Currently, most flat panel HDTV sets still use cablings to connect to set top box or other devices such as DVDs, BlueRay devices or VCRs. The cabling requirements limit the flexibility of HDTV installation and the appearance. So, there is a market demand to find solutions that eliminate or minimize use of cables. Some companies proposed wireless HDTV solutions in the 60 GHz spectrum, whereby delivering raw data wirelessly to the HDMI port, which is a standard HDTV interface. Although there is some progress in this area, the performance and cost of this solution still poses design and operational challenges.
On Oct. 15, 2008, the FCC's engineering office released a report that spells out the rules the devices must meet in order to use the white space, the main requirement being not to interfere with the primary services active in the respective area. Thus, the signals radiated by any white space device operating in the ATSC spectrum must follow the FCC regulations so that the quality of the primary services such as TV broadcast, wireless microphones, or other emerging services already deployed or which will be deployed in that area will not be degraded by these new services. The new white space devices should be designed so as to not affect the TV tuner sensitivity and the TV receiver performance specified by the Advanced Television Systems Committee (ATSC) standards. The specification uses the term “white space etiquette” for this set of regulations that must be accounted for when designing and using white space devices. For conformity with these requirements, FCC requires both fixed and portable devices to include geolocation capabilities and use an FCC database of TV signals and location of venues such as stadiums and churches that use wireless microphones. These database and geolocation capabilities would, in theory, prevent interference with broadcast TV stations and wireless microphones and ensure compliance with FCC rules.
The mobile industry is considering using the white space by developing standards on technologies convergence into an architecture that is comfortable, easy to use and attractively priced. For example, the IEEE 802.22 Working Group, formed in 2004, received the mandate to develop a standard for Wireless Regional Area Networks (WRAN). The mission for this technology is to provide rural area broadband services to single-family residential, multi-dwelling units, small office/home office, small businesses, etc. The standard will be used by license-exempt devices in the spectrum allocated to the TV broadcast service on a non-interfering basis. The 802.22 draft specifies that the network should operate in a point to multipoint configuration, where an outdoor installed access point (AP) will control the medium access for all the customer premise equipment attached to it, while avoiding interference with the broadcast services. One key feature of the WRAN APs is the capability to perform a distributed spectrum sensing, where the customer premises equipment will be sensing the spectrum and will be sending periodic reports to the serving AP informing it about what they sensed. Based on the information gathered, the AP will evaluate whether a change is necessary in the channel utilized, or conversely, if it should stay transmitting and receiving over the same one. OFDMA is proposed as the modulation scheme for transmission in uplink and downlink. Channel bonding is also specified for cases when higher bit rates and distances are needed.
However, the 802.22 draft proposes use of the white space only in chunks of 6 MHz (the width of a TV channel specified by the ATSC standard) and does not allow for finer granularity. Also, it requires high power transmissions in both base stations and terminals so as to cover an area with a 30 km radius. This results in inefficient use of bandwidth (which is a valuable resource) for the case when only a portion of a 6 MHz channel is actually needed. For instance, when a wireless microphone application occupies a few hundreds kHz bandwidth from a 6 MHz piece of spectrum, the reminder of the 6 MHz may be wasted. As well, the bandwidth resources may be inefficiently utilized when the broadband market is in populated areas such as homes or shopping malls etc.
Therefore, there is a need to provide an inexpensive and efficient way to broadcast multimedia content within a specified area using wireless solutions. There is also a need to set overall rules (etiquette) on how to use the white space spectrum that is reserved but not used by the primary services in a certain area, without affecting operation of the existent services.